1. Field of the Invention
The present invention relates generally to an apparatus for measuring the moisture content of moving bulk material and, more specifically to an apparatus for measuring moisture content and bulk flow rate of cotton and other materials while they are being transported on a belt conveyor.
2. Description of the Prior Art
In processing cotton, its moisture content is always of critical importance. This is true whether an operator is drying cotton in order to preclean it in a cotton gin, preparing to measure the fiber properties of lint cotton at a classing office, or preparing to spin the cotton in a spinning mill.
The most popular method of measuring cotton moisture content is to measure its electrical resistance or its reciprocal, electrical conductivity. This method is reliable because the specific resistance of cotton fiber increases by a factor of about 5.5 for every one percent decrease in moisture content. The method is being used with good results on unprocessed seed cotton. Since such material has not been dried, the reading is indicative, not only of fiber moisture, but of the probable moisture level of the cottonseed.
The resistance method is particularly desirable for measuring after-drying moisture in seed cotton. The drying process dries the cotton fiber, which is still attached to the seeds, but has very little effect on the moisture content of the seeds. The resistance method in this case is highly selective, measuring lint moisture, the variable being affected, and ignoring an extraneous variable, seed moisture.
The resistance method is also adaptable to making continuous measurements on flowing streams of cotton, instead of taking intermittent samples. Certain precautions and conditions must be observed in utilizing this method, however, which have led to problems in the devices of the prior art.
It is important that the measuring electrode be pressed against the cotton with a uniform pressure. Variations in this pressure will give an apparent change in resistance which is not caused by a change in moisture content. If the cotton being analyzed is rather dry, another factor which must be considered is the generation of static electricity due to movement of the cotton, which may affect the accuracy of resistance readings.
It is common practice in textile mills and paper mills to utilize the resistance method to measure moisture in moving webs of material. The electrode is usually a roller type where the web is moving at a fast rate. For slower moving webs, electrodes which slide on the moving web are often used.
Samuel Jackson used the roller electrode method of measuring cotton moisture in a moving bed dryer in a cotton gin in Madison, Ala., in 1966. The control system modulated the temperature of the drying air to yield a constant final moisture content at the end of the dryer bed. It used a cylindrical drum about 12" diameter and 24" wide mounted on an axle which, in turn, rotated about a point well above the bed of cotton to accommodate varying depths of the cotton bed. When lack of cotton let the drum come within 1" of the moving steel dryer apron, a limit switch stopped all control action.
The electrode's cylindrical surface was covered with a copper-glass-epoxy etched electrode which was connected, through slip-rings, to the electronic measurement and control devices. The electrode had arrays of copper strips with about 10 mm of exposed insulation between each strip. Three such arrays were connected in series so contact by pieces of highly conductive trash would not drive the moisture reading entirely upscale. This control system was used for about 20 years.
Several prior art references are also known which teach methods of measuring the moisture content of seed cotton. One method of obtaining an accurate moisture reading of seed cotton coming into a cotton gin is described and claimed by Neitzel in U.S. Pat. No. 3,114,613. This involves using a pneumatic cylinder to compress seed cotton in a feed control bin against an electrode on the other side of the bin. This is not a continuous process, but depends on intermittently sampling the cotton. This apparatus did attempt to solve the problem of obtaining uniform pressure between the electrode and the cotton being analyzed. The use of a pneumatic cylinder to intermittently sample cotton by pressing a sample mass against a side wall was also the subject of U.S. Pat. No. 5,125,279, to Anthony.
In many modern cotton gins, the incoming seed cotton from the module feeder is conveyed by air directly into the gin's drying system. Only the small percentage of cotton which comes to the gin in trailers passes through a feed control bin, so the method described in the above-referenced patents cannot be used on the majority of the cotton being processed today. In order to solve this problem, Anthony describes an improved "paddle sampler" in his later issued U.S. Pat. No. 5,087,120. The "paddle sampler" intermittently gathers a sample of cotton from an airborne stream on a "paddle" which slowly rotates 180 degrees against the direction of flow. The paddle then presses the sample against a sensing electrode with constant pressure.
Unfortunately, this apparatus did not solve the problem of measuring seed cotton while it is being conveyed in hot air. The stream of hot air blasting against the sample while it is being gathered on the paddle dries it so much that the moisture measurement is not usable. Where the cotton is conveyed by ambient air, however, the paddle sampler method can be used to give accurate moisture readings. Since cotton is usually conveyed from the module feeder in a stream of hot air, a need existed to develop another method of measuring its moisture content.
Although designed for gathering cotton from a flowing air stream, the paddle sampler has been used with success in gathering samples of seed cotton from the enclosure of a module feeding disperser, where the disintegrated cotton is ballistically propelled. This still leaves the problem, however, that due to its location, it only measures moduled cotton and not trailer cotton.
Ordinary electrodes with no means of compression are widely used in feed control bins and in the hoppers above the extractor feeders in cotton gins. They have been successfully used on trailer cotton in the feed control bins. Since there is a wide range of moisture content in incoming cotton, the enhanced accuracy obtained by a compression device is not provided, however, in all cases. Fast input into the dryer control system for changes in moisture level is most important.
The use of compression apparatus is almost essential in the extractor feeder hoppers, where the range of moisture contents being measured is low and narrow, and greater precision is needed. Also, the drier cotton often has static charges which greatly distort the reading. Holding the sample against the electrode for some time allows static charges to dissipate before the reading is accepted.
It is accordingly an object of the present invention to provide an apparatus for making continuous moisture measurements on cotton or other material being transported by a belt conveyor which overcomes the above mentioned deficiencies of the prior art devices.
Another object of this invention is to provide an arrangement whereby uniform pressure is exerted on a sliding moisture sensing electrode.
Yet another object of this invention is to provide a sliding moisture electrode which is resistant to the disturbing influences of static electricity.
Another object of this invention is to provide an electrical signal which is directly proportional to the moisture content of the material being transported on a belt conveyor.
Yet another object of this invention is to provide a scalar electrical signal indicative of the bulk flow rate of the material transported on a belt conveyor, doing so with the same apparatus which measures moisture content.
Still another object of this invention is to provide those features described above, doing so with apparatus which is dependable in design, economical to manufacture and simple to install.